Couple things.

First off, the Auroral Tabard example puts crit rate on it. There are caps for attributes at each ilvl, and the tabard is already at that cap in crit rate. If you bypass this system, then the only thing worth putting on gear is STR/DEX/INT/MND because they are so overpowered vs the secondary attributes.

Each piece of raid/dungeon gear and HQ crafted gear gets main attributes and two secondary stats, the main attributes and one secondary are at the cap, the other secondary is at ~70% of the cap. Raising the ilvl by 5 won't raise these caps by very much.

Second, instead of the complex master materia system to increase the amount of materia, they need to simply make dungeon gear convertible.